The proposed research program is aimed at defining changes which occur in lymphocyte subpopulations, associated with spontaneously occuring and experimentally induced neoplasias. These studies will be performed in AKR/J mice with a high incidence of spontaneously occuring lymphocytic leukemia, and in mice (BALB/cJ) undergoing growth and spontaneous regression of a tumor induced by inoculation of the Moloney sarcoma virus. These systems are readily subject to manipulation by immunosuppressive and immuno-stimulatory agents, making possible the study of models for the control of leukemogenesis and tumorigenesis. Experimental approaches include: Evaluation of peripheral and central lymphocyte populations from normal, pre-leukemic, leukemic and tumor-bearing animals with respect to 1) homing properties as measured by in vivo distribution of Cr51 labelled cells, 2) surface characteristics, e. g. theta, TL antigen, immunoglobulin, complement receptors, 3) response to mitogens, e.g. PHA, ConA, PWM, LPS, and 4) immune competence, as measured by GVHr and MLR responses. Parallel studies will be conducted in mice subjected to treatment with 1) immunosuppressive agents, e.g. ALS, corticosteroids, thymectomy, and 2) immunostimulatory agents, e.g. adjuvants, BCG, interferon inducers, and thymosin. These studies will be extended to investigation of first passage AKR leukemic cells, and other tumor models, as the data warrant.